The present invention relates to methods for determining the relative immunogenicity of exogenous antibody variants comprising a) creating a non-human animal, which is transgenic for a standard antibody, b) contacting said transgenic non-human animal with an exogenous antibody whereby said exogenous antibody is a variant of said transgenic standard antibody of a), and c) determining the immune response of the transgenic non-human animal elicited by the exogenous antibody of (b).